The long-term goal of this proposal is to analyze the functional properties and modulation of GABA-mediated synaptic connections in the rat visual cortex and relate these properties to the role of inhibition in cortical processing of information. We will use dual recording from pairs of synaptically connected neurons together with recordings of miniature IPSCs and techniques for rapid application of agonist onto excised patches to study two main specific aims: 1. Unitary Inhibitory GABAergic Synapses Paired recording will be used to estimate the reliability of inhibitory synaptic transmission in the visual cortex. The second goal is to assess the impact of individual inhibitory neurons on the activity of their postsynaptic targets. The third goal is to study the differences of the synaptic responses generated by different classes of inhibitory neurons. We would study the postsynaptic response generated by activation of axo-axonic axo-somatic and axo-dendritic GABAergic neurons. 2. GABAA receptors Recording of miniature IPSCs together with rapid application of GABA to excised outside-out patches will be used to study the functional properties of GABAA receptors in different types of pyramidal and nonpyramidal neurons. The second goal is to find if there are functional differences among GABAA receptors at different neuronal compartments. We will study the response of dendritic, somatic and axonal outside-out patches to rapid application of GABA.